A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Traditionally, substrates used in lithography have been one of a relatively small number of sizes and shape. For example, a traditional substrate may be substantially circular in shape, with a diameter of 200 mm (8 inches) or 300 mm (12 inches). The substrate may be, for example, 200 μm thick. However, as technologies which use and depend on lithography develop, the shapes and sizes of substrates used has also changed. Substrates used in modern lithography may be very thin (for example 50 μm, 40 μm or less), have pits (cavities) in the underside of the substrate, have slots through the substrate or have extremely high bow or warp. Substrates may have rims around their perimeter. The substrates may be irregularly shaped (i.e. non-circular, for example square in shape). In short, the shape and size of substrates used in modern lithography are evolving with the technology which uses the substrates.
In order to accommodate different shapes and sizes of the substrates, lithographic apparatus used to pattern the substrates may need to be modified, or new lithographic apparatus created. For example, some lithographic apparatus incorporates equipment which is specifically shaped for dealing with certain sized substrates. Thus, without modification, such lithographic apparatus cannot be used to apply patterns to a non-standard sized (i.e. a non-traditional) substrate.
A proposed way of overcoming some of the problems of using existing lithographic apparatus to apply a pattern to a non-traditional substrate is the use of what is known in the art as an intermediate substrate carrier (or substrate carrier, for short).